The present invention is related to the field of thin-sheet optics for automotive exterior lighting applications, including night vision systems.
Conventional lighting systems used in automotive vehicle applications such as headlights, taillights, and active night vision systems utilize an incandescent bulb with a reflector. The light emitted by the incandescent bulb is generally collimated by the reflector. The incandescent bulb may be used to generate light in the visible spectrum for headlight and taillight applications. Active night vision systems typically require near-infrared emissions that are compatible with solid state CCD or CMOS cameras to illuminate the scenery.
Advances in the solid state lasers have given rise to thin-sheet lighting systems for use in taillight and active night vision systems. The thin sheet systems require less space than bulb and reflector systems. Furthermore, laser diodes are more energy efficient and reliable than incandescent bulbs. A challenge in thin-sheet lighting systems is to rapidly spread the laser light over a sufficiently wide area to meet spatial illumination and eye safety requirements required under law. Many different approaches have been suggested to expand the point source of laser light uniformly over several square inches of an exterior optical surface.
U.S. Pat. No. 5,791,757, issued to O""Neil et al. on Aug. 11, 1998, discloses a lighting system that uses a uniform thickness thin-sheet optical element. This optical element has a plurality of micro-optical wedges that collimate and direct a divergent laser light emitted from multiple fiber optic bundles. Diffractive optical elements are disposed intermediate the thin-sheet and fiber optics to direct the laser light to predetermined regions of the plurality of micro-optical wedges. The diffractive optical elements guide the light to the micro-optical wedges either in a direct path, or by bouncing the light off the exterior side of the thin-sheet opposite the micro-optical wedges. The optical efficiency of this approach could be improved upon if the diffractive optical element could be eliminated. Design complexity could be reduced if each of the micro-optical wedges did not have to be designed to receive the light from a different incident angle.
The present invention is an optical element, a lighting system utilizing the optical element and a method of manipulating light from a source to provide an illumination pattern suitable for use in a night vision system and exterior lighting applications. Optical efficiency is maximized in that the light passes through as few as two surfaces, and is reflected only once by the optical element. Design complexity is minimized as all reflective surfaces in the optical element can be formed with the same orientation.
Light emitted from the source has a naturally divergent emission pattern. A predetermined distance between the source and optical element is provided to allow the emission pattern to spatially expand prior to reaching the optical element. The spatially expanded emission pattern partially or totally fills an input surface of the optical element.
Light enters the optical element through the input surface. The light exits the optical element through an output surface that is approximately perpendicular to the input surface. A stepped surface of the optical element is angled between the input surface and output surface to intersect the light. Multiple facets are formed in the stepped surface to reflect the light toward the output surface. The facets, input surface, and output surface are arranged such that light reflects from only the facets in passing from the input surface to the output surface. A net result is that the divergent emission pattern of the light emitted from the source is manipulated into a broader illumination pattern emitted from the output surface.
In one embodiment, the facets are arranged in a striped pattern paralleling a narrow dimension of a rectangular shape. Here, the input surface has a curvilinear shape to collimate the light in a first plane parallel to the output surface. In another embodiment, the facets are arranged along arcs about an axis normal to the output surface. Now, the input surface allows the light to continue to diverge in the first plane to fill the arc. In both embodiments the curvilinear input surface or external lens may collimate the light in a second plane perpendicular to the output surface. Collimating the light prevents the light from striking outer surfaces of the optical element prior to reflecting from the facets. Where necessary, a second optical element may be disposed between the source and the optical element to provide the proper divergent emission pattern at the optical element.
Accordingly, it is an object of the present invention to provide an optically efficient optical element, lighting system and method for manipulating a light having a divergent emission pattern to produce a broader illumination pattern wherein the light is reflected from only once inside the optical element.
These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings.